(1) Field of the Invention
The present invention relates to a photosensitive composition and a pattern-forming method. More particularly, the present invention relates to a photosensitive composition suitable for formation of a phosphor screen of a color picture tube and a pattern-forming method using this photosensitive composition.
(2) Description of the Prior Art
In a so-called black matrix color picture tube, the size of each of phosphor dots on a face plate is smaller than the irradiation areas of scanned electron beams, and a non-luminous light-absorbing substance such as carbon is filled in voids among respective phosphor dots. Also in a so-called black stripe color picture tube where the phosphor is applied in the form of stripes, the size relation between the phosphor stripes and the irradiation areas of scanned electron beams in the lateral direction is the same as described above with respect to the black matrix color picture tube.
As the method for forming these color picture tubes, there has been adopted, for example, a post-etching method. According to this known post-etching method, dots of a photosensitive composition is prepared at positions, in which a phosphor of a phosphor screen is to be arranged, by using a shadow mask having a small hole diameter, voids among the respective dots are filled with a non-luminous light-absorbing substance and the dots are peeled and removed, and then, red, green and blue phosphors are filled in sequence to form a phosphor screen. Separately, the above-mentioned shadow mask is etched with an acid or the like to increase the hole diameter and the shadow mask is assembled in a color picture tube. This method, however, is still defective in that the hole shape is deformed at the step of etching the shadow mask or distortion is caused in the mask at the heat treatment to be carried out after the etching treatment.
As another conventional method, there has been proposed an optical method not conducting the post-etching treatment, for example, a method using a rotary light source. This method is advantageous in that etching of the shadow mask after formation of a phosphor screen need not be carried out. However, this method still involves problems to be solved. For example, a special light source is inevitably used, and if the hole diameter of the shadow mask is increased beyond a certain level, the portion between two dots is irradiated redundantly and therefore, the irradiation quantity exceeds a level corresponding to the minimum degree of cross-linkage of the photosensitive composition, with the result that the two dots are interconnected to each other. One of the inventors of the present invention has already proposed a pattern-forming method suitable for formation of such phosphor screen, in which the above disadvantage is eliminated, in the specification of U.S. Pat. No. 4,086,090. According to this method, a photosensitive composition comprising an acrylamide/diacetone-acrylamide copolymer (hereinafter referred to as "AA/DAA copolymer") and a water-soluble aromatic bisazide compound is used to form a pattern having an area substantially equal to or smaller than the irradiation area. According to this method, a phosphor screen free of interconnection of dots can be prepared by using a shadow mask having a large hole diameter from the beginning without conducting the post-etching treatment.
The reason why such method is possible is that the above photosensitive composition has a reciprocity law failure. By the term "reciprocity law failure" is meant the characteristic in which the following relation is established among the intensity i of light radiated on the photosensitive composition, the exposure time t and the resulting degree B of cross-linkage: EQU B=f(i.multidot.t.sup.p)
wherein p is Schwarzschild's constant which is in the range of 0&lt;p&lt;1.
In ordinary photosensitive compositions, p is equal to 1 and the relation of B=f(i.multidot.t) is established.
Practically, as the value of p is smaller than 1, occurrence of interconnection of dots is more reduced and dots having a desirable size can be advantageously formed. A preferred range of p is 0&lt;p&lt;0.76, and it is preferred that irradiation be carried out under this condition.
This method is an excellent method for forming phosphor screens, and the above photosensitive composition has a high sensitivity and is very suitable for use in carrying out the above method.
However, this photosensitive composition is still insufficient in that a relatively long time is required for development.